Carrot Seeds

The
Carrot plant (Daucus carota L.) is biennial and develops, in its second
year, 'umbels' which are groups of flowers which
produce seeds. D. carota var sativus is a herbaceous biennial plant grown as an
annual. In the first year, seedlings emerge with two strap-like leaves which are
the cotyledons, followed by rosettes of doubly compound leaves arising from the
crown.

From the hypocotyl, a tap root develops. Initially, the plant produces top
growth, which supplies carbohydrates to the swelling hypocotyl. High
temperatures increase respiration in the leaves which reduces colour development
and sugar accumulation. Low temperature initiates flower development and reduces
carbohydrate accumulation in the hypocotyl. Most often, the plant will not
initiate a flower head until the second year of growth and a chilling period.

Breeders aim to derive cultivars with early maturation, high yield,
high beta-carotene content; the ability to set seeds under poor
conditions; uniform root size, shape and colour; small tops, tender roots;
improved flavour, texture, sugar content and dry matter; resistance to
cracking and breaking during harvest, roots that taper uniformly, slowness
to bolt; tolerance of poor soil and climate; wide adaptability; resistance
to disease, especially leaf blight, black rot, powdery mildew, bacterial
soft rot, and and to pests including caterpillars and carrot fly.

A carrot may have more than 1000 flowers. The outer flowers mature first,
though the flowers in the core have the most fertile pollen. Each flower has
five sepals, five stamens and two carpels. Each carpel has two ovules. Because
the pollen and ova of a single perfect flower are fertile at different times,
the carrot is not normally a self-pollinator.

The inflorescence is an umbel, with individual flowers maturing at staggering
intervals. Cross-pollination is essential for seed development. The Apiaceae
family derives its name from its affinity for attracting bees, which are the
primary pollinator. D. carota seeds are tiny, and are covered with a fleshy
mericarp that must be removed prior to seeding. Due to cross-pollination,
variability is great in plants.

Flowering in biennials is stimulated upon vernalization (a period of extended
exposure to low temperatures, usually experienced under winter conditions).
Vernalization is a physiological response of phytohormones present in shoot
apical meristems; in a carrot the shoot apical meristem is located in the layer
of cells of the compressed stem found at the interface between the carrot root
and the interior of the rosette of leaves (the tissues usually cut off before
eating). When the cold period is satisfied in a biennial, a cascade of events
occur, leading to flowering.

Carrots remain in a juvenile non-flowering form until subjected to cold
exposure. Carrots planted in last year’s autumn garden and over wintered are still
in their juvenile stage of growth and the root is still edible; but soon, a
spring flush of shoot growth will occur in tissues that have been induced to
flower commencing the irreversible transition from the juvenile (vegetative)
edible stage to reproductive maturation (flowering).

The birds nest shaped fruit cluster has a remarkable mechanism for seed
dispersal. The stalks are hygroscopic (readily taking up and retaining
moisture), so that when conditions are dry and suitable for dispersal, they bend
outward, exposing the fruits to wind and animals;when conditions are wet, they bend inwards, forming the familiar birds nest structure, which protects the
seeds.

Classical studies conducted in 1937 by M. K. Chailakhyan proposed that the
floral stimulus is a hormone called “florigen.” A single compound has never been
isolated; however, subsequent numerous physiological studies of floral
transitioning have identified several putative signals that stimulate flowering:
the carbohydrate sucrose and the plant hormones cytokinin and gibberellin. In
response to cold exposure, these compounds are translocated from leaves to the
rosette of the shoot apical meristem.

Seems science is never simple. In science, when one question is answered,
other facets become exposed, leading to further research. This is the fun and
excitement of science. The story of flowering in carrot is a little more
complicated than just vernalization of carrots, the cold-induced flowering in
response to hormonal stimuli. Genetics of an organism must be also considered.

There is quite a lot more information about the influence of
Dutch agriculturists and their role in Sandwich inGarden
seeds in England before the late eighteenth century: I. Seed growing By Malcolm
Thick, Agricultural History Review, 1989) -full
copy here - pdf)

Seeds are formed from carpels. They are tiny and covered with
a spiny, hooked, and slightly curved mericarp. The mericarp contains a
characteristic oil which inhibits seed germination, requiring the removal of the
mericarp before planting.

Seeds are highly variable due to cross-pollination and have
undergone extensive breeding programs to increase uniformity. Hybridization,
however, has not produced consistent results. Seed development and vigor are
determined by the conditions under which they are formed. A larger seed
(embryo) will have a more rapid emergence and produce a stronger seedling. This
is important in that the seed is slow to germinate and the young seedling is
slow in the initial growth phase. There are approximately 23,000 seeds per
ounce.

Read this informative article in the Wisconsin Magazine for Life Sciences on
how to
make a purple carrot here. It also explains how the breeders have to cross
several times over many years to tease out favourable traits and create a carrot
with the desired qualities (eg colour, disease resistance etc).

Carrot seeds are not true seeds in a botanical sense but are dry
fruits called 'schizocarps'.
The Carrot is not a fruit in the common understanding, so there are no seeds inside
or on the carrot.
The part of the carrot that you eat grows in the ground, usually with the wide
end
of the carrot just at the surface of the soil. The round mark you can see on
that
end of the carrot is where the leaves used to be - a big soft bunch of deep
green
leaves that look a bit like a fern.

Then the carrot is ready, it sends up a tall
stem, which produces flowers, and eventually seeds. The seeds are very small, on
average between 1 and mm in length and brownish is colour. Depending on the
variety there are approximately 8000 seeds in half an ounce of seeds, so there are approximately
250,000 in a pound, roughly 2500 would fill a teaspoon.

The
birds nest shaped fruit cluster of carrot has a remarkable mechanism for seed
dispersal. The stalks are hygroscopic (readily taking up and retaining moisture)
so that when conditions are dry and suitable for seed dispersal, they bend
outwards exposing the fruits to wind and animals; when conditions are wet, they
bend inwards forming the familiar nest structure which protects the seeds.

Now for the bad news - If you are planning to grow carrots, letting one go to
seed
may not be the best solution. Carrots are biennial - that means they take two
years
to reach maturity when they can produce seeds. Secondly, the vast majority of
carrots that you buy from the supermarket are F1 hybrids. That means the seed
comes
from TWO parents who are different. (One may be big and fat, while the other is fast growing and a nice colour.)

By using pollen from one to fertilise the
flowers
of the other, the plant breeder and seed specialist aims to produce carrots with distinctive
characteristics which are appropriate to the market. For example long and
thin, deeper colour and consistency, or resistance to carrot fly, drought etc. The resultant carrot
aims to be just what the farmer wants, but
there are usually two problems for the consumer - The carrot may not have taste
(low on the farmers list of priorities, because you can't cook and taste before
you
buy!!) and in the vast majority of cases, F1 hybrids are sterile.

If you grow an
F1 carrot and harvest the seed ( after two years!!) they may very well not grow.
In some cases you just get no flowers or seeds at all, or a sterile plant or a
plant totally unlike its original. (read more
below)

Carrot Seed Production a paper by P.W.
Simon, USDA, ARS, Department of Horticulture, University of Wisconsin, Madison,
WI 53706 USA

Production of carrot seeds is a two-year project making it
much more difficult than seed production of annual crops. Sound roots must first
be produced (first year), these roots must be either harvested and carefully
stored in a refrigerator or left in the field (if your winters are not too
severe), these cold-treated (vernalized) roots must be grown and supplied with
pollinating insects when flowering, and seed harvested. Carrot seed must be
produced where no wild carrot (Queen Anne’s Lace) is growing.

Procedures

1. Grow vigorous plants.

Grow plants at the same time of year and the same way you
usually would. Weak or diseased plants are subject to storage loss during
vernalization and they set few seeds. Plants with pencil-sized roots may be
large enough, but larger roots are preferable.

2. Vernalize roots.

Carrots require 6 to 8 weeks cold treatment (2 to 5°C) for
floral induction. Cool growing conditions can reduce the cold storage
requirement. Roots can be vernalized in two ways. If carrots are a summer crop
in your area, you can simply leave roots in the field over your winter season if
your climate provides at least 10 weeks of temperatures below 15°C but where
temperatures are not so cold that roots will freeze to death. Early in the
growing season plants should be thinned to at least 5 cm apart. Dead or dying
leaves must be removed and tops can be cut back at your usual harvest time to 5
cm to reduce transpiration and covered with mulch if necessary. When warm
weather resumes, remove mulch if necessary and leaves will regrow and after
several weeks a seed stalk will appear. This is the "seed-to-seed" method of
carrot seed production. Losses are often very high with this method and
off-types of roots cannot be eliminated since roots are not harvested and
visually examined. The "root-to-seed" method is more reliable. Harvest roots
when you usually would and discard off types. Trim tops back to 2 to 4 cm, air
dry until no surface moisture remains, pack in paper bags with an equal volume
of wood shavings, and place paper bags in closed polyethylene bags at 2-5°C.
Puncture plastic bags after several weeks when water droplets accumulate inside
the polyethylene film. Better storage survival is realized if prior to
refrigeration, lateral and fibrous roots are removed, soil is removed by washing
gently, and senescing leaves are removed. Even with these precautions carrots
are often very susceptible to pathogen infection during storage. In commercial
production, roots are dipped in fungicide before vernalization but this practice
is not advised without extreme caution.

3. Grow vernalized plants.

For the "root-to-seed" method, plant vernalized roots when
you would plant seed in the spring, taking care to keep plants well-watered but
not in standing water. Seed stalk development will be evident in 4 to 6 weeks.
Control of microbial (Alternaria, Cercospora, aster yellows, motley dwarf) and
insect pests (aphids, spider mites, lygus bugs) is essential to assure seed
production. It is very difficult to produce carrot seed where warm humid
climates favor microbial growth. Note: Carrot seed can only be produced true to
type if wild carrot (Queen Anne’s Lace) is not growing nearby since wild carrot
will intercross and yield white-rooted plants.

4. Pollination.

Pollination is best performed by introducing bees or flies
for pollen transfer during the period of receptivity. Natural populations of
bees and other insects will sometimes be adequate. As an alternative, pollen
movement is possible by hand or brush but seed set will often be low. Within 4
to 6 weeks after pollination the developing seed turns brown. Harvest (before
the seed shatters) into paper bags to dry completely. Late-season rains can
reduce seed yield drastically. Remove spines from dry seed by rubbing. Seed is
now ready to plant since carrot has no seed dormancy. Store dry seed
refrigerated in a moisture-proof container.

Reproductive Biology (source P Simon)

Carrot is an outcrossing, insect-pollinated diploid
(2n = 2x = 18) species. It typically does not flower during the vegetative
phase of its life cycle when the storage root forms and grows for 60 to
150 days (or more) depending upon environment andgenotype. Early plant
growth is slow as seedlings are established but then growth israpid until
interplant competition and seasonal climatic changes to suboptimal
temperature limit growth (Rubatzky et al.. 1999).

As a biennial crop, this vegetative phase of carrot
life cycle is essential to successful crop production, but carrot breeders
require flowering plants. Cool temperature is the primary stimulus that
initiates carrot flowering so that plants exposed to cold weather in the
field, or harvested and refrigerated, will make the transition from
vegetative phase and initiate flowering. The amount of cold exposure
necessary for this transition varies widely across diverse germplasm, with
varieties developed for warmer climates generally requiring less cold
before flowering begins. Carrots can be handled as an annual crop in
breeding programs, typically raising a winter root crop in warmer
production areas, harvesting and vernalising that crop at least 6 weeks in
refrigerated storage, and then producing a summer seed crop in a cooler
area to complete the cycle within one year.

Carrot flowers are protandrous (a plant, in which the
male reproductive organs mature before the female reproductive organs) and usually perfect,
forming at most two seeds per flower. In addition to hermaphroditic
flowers, there are also male-only flowers that occur at increased
incidence with a rise in the order of umbels. A single carrot plant
typically produces several hundred to several thousand flowers on multiple
umbels over a few weeks (Rubatzky et al., 1999).

Heirloom versus hybrid seeds

The big difference in vegetable seeds is whether they are heirlooms (aka
heritage) or
hybrids. Heirloom seeds are those that are open-pollinated, a variety that will
breed ‘true to type’ from one generation to the next. Seeds from heirloom vegetables are true to type,
meaning that you can save the seed from a certain plant and it will carry their
parents’ genetic material and plants grown from them will bear their
characteristics again next season.

F1 hybrid seeds refers to the selective breeding of a plant by cross
pollinating two different parent plant varieties, both of which contribute
genetically to the offspring. In genetics, the term is an abbreviation for
Filial 1 – literally “first children.” Seeds
saved from F1 hybrids will not normally produce a plant with the characteristics of
the parent.

Hybrid vegetable seeds are created by artificially crossing two or more
varieties of a certain plant. Hybrid vegetables are what one typically sees
being sold in the your local garden store, those rows of bright, uniform carrots
are probably grown from hybrid seeds.

One big disadvantage with hybrids is that you cannot save the seed: resulting
seeds may be either sterile or produce a plant totally unlike its original.
Although hybrid plants produce fruit that ripens at the same time and may be
more resistant to pests or diseases, they’re not selected for their taste. They
are typically selected for appearance and shelf life. Hybrid seeds are typically
more expensive than heirlooms, too.

Home gardeners will likely be more satisfied with heirloom vegetable
varsities for the flavour they deliver, and the sheer variety of vegetable types
that are available. Blue potatoes, purple carrots, and orange tomatoes are not
unusual among heirloom varieties. And perhaps best of all is that gardeners can
save the seed from their heirloom vegetable plants, and continue to grow them
year after year, and pass them on the family and friends well into the future.
The same simply cannot be said for hybrids.

The 1600+ accessions in the UK Genetic Resources Unit carrot collection include
varieties, landraces and related wild species. The collection is used by
researchers and breeders from around the world to understand trait genetics and
introduce novel material into breeding programmes.

The Umbellifer database was established at Wellesbourne (Warwick UK) following
the first meeting of a European carrot group under the auspices of the ECPGR in
Kraków, Poland in 1997 and was updated by the Umbellifer Working Group in 2013.
The database includes nine genera including Anethum L. (dill), Apium L.
(celery), Carum L. (caraway), Chaerophyllum L. (chervil), Coriandrum L.
(coriander), Daucus L. (carrot), Foeniculum Miller (fennel), Pastinaca L.
(parsnip), and Petroselinum Hoffm. (parsley). The European Umbellifer DataBase (EUDB)
was updated using data from EURISCO and national programmes. The data are
available in Microsoft Excel format using the EURISCO Multi-crop Passport
Descriptors. The database is maintained by the Warwick GRU and
available for viewing/download here.

Carrot seeds do not mature uniformly within a single plant. Seed maturation
depends on the positions of flowers on the maternal plant, from which seeds are
originated. Flowers and seeds in different orders (primary, secondary and
tertiary) of umbels exhibit various levels of maturity.

Each umbel consists of multiple 'rays', groups of flowers. Maturity of rays
depends on their positions (outer, middle and inner) in an umbel, with the outer
maturing first.
The birds-nest-shaped fruit cluster (umbel) of the carrot has a remarkable mechanism for
seed dispersal. 'lThe stalks are hygroscopic, so that when conditions are dry
and suitable for seed dispersal they bend outward, exposing the fruits to wind
and animals; when conditions are wet, they bend inwards, forming the familiar
bird’s nest structure, which protects the seeds.

Carrots are biennial, flowering in their second year of growth. In areas with
mild winters, leave your carrots in the ground, mulching them heavily. The
foliage will die back in autumn, but will then re-sprout and start to flower in
the spring. In colder areas, dig up your carrots in the autumn, and select the
best coloured and shaped roots. Twist off the foliage, and store the roots in a
box of dry sand in a frost free place, making sure that they don't touch. In
spring, replant the roots, and they will re-sprout and flower.

If you want to maintain a carrot variety effectively, you really need to save
seed from at least 40 good roots to maintain good genetic diversity. If you have
too small a genetic pool, you will end up with small, poor quality roots in a
very few generations.

Carrots grow into big plants waist high or taller, producing successive branches
with large flat umbels of flowers. They are insect pollinated, and need to be
isolated from other flowering carrot varieties by at least 500m in an open field
situation. This is not normally a big problem, since few people let their
carrots go to seed. However, they will cross with wild carrot (Queen Anne's
Lace), giving thin white useless roots.

As with all insect pollinated crops, barriers such as houses, tall hedges and
other high crops can affect insect flight paths drastically, so you don't
necessarily need to eliminate all Queen Anne's Lace within a 1/2 km radius; but
do watch out for any white roots in subsequent generations and get rid of them.

Watch the very informative video from Heritage Seed Library (part of Garden
Organic) on how to collect carrot seeds.
Here. (YouTube video)
or download the seed saving guide here (pdf)

Carrot Seed under the
microscope

To harvest your carrot seed, keep an eye on the umbels of flowers, and cut them
off with secateurs as they start to turn brown and dry. Carefully cut the heads
and place them in a small paper bag and then leave them alone until the drying
is complete. Small plastic containers or glass jars can also be used, but be
careful. The same airtight lid that will protect your dried seeds will also hold
the moisture of the not quite dry seed heads and that can lead to the seeds
going mouldy. Store your unlidded containers in a safe dry place. Seal once
fully dry.

If you have plenty of
plants, just save seed from the first and second umbels of flowers to appear on
each plant, as these will give the biggest and best seed. Dry the seed heads
further inside, and then rub them between your hands or in a sieve to separate
them. You will notice that the seeds have a 'beard' which is removed in
commercial seed to make them easier to pack.

You can sieve the seeds further to remove more of the chaff, but there is no
need to get the seed completely clean - just sow slightly more thickly to allow
for the chaff mixed in.

Dried carrot seed is relatively short lived, but if it is stored somewhere cool
and dry, it should give good germination for 3 years. Seeds can be safely stored
for at least three years. Place seeds in jars, manila envelopes, cloth or mesh
bags, plastic containers, or foil envelopes. The best containers are air-tight,
such as a sealed glass jar, metal can, or foil envelope. Protect seed from
sunlight. Store seeds in a cool (below 15 °C is ideal), dry location. Place the
seeds in a refrigerator for long term storage.

For short-term storage, keep the seeds in a cool, shady and dry place.

What do seeds contain and how do they work?

A seed is the product of a fertilised ovule (egg). It is the means by which the progeny of a plant can be spread. The seed contains the embryo from which a new plant will grow. The seed contains a supply of food called the endosperm that is used by the new plant to develop. The whole seed is covered in a seed coat known as the testa.
Seeds are found in a great variety of types.

The testa protects the contents of the seed. For the seed to grow the testa
needs to split. The seed imbibes water which causes it to swell and split open
the testa. The seed coat varies between different types of seed, which in turn
affects, the uptake of water. Some seed coats are very thick and need to go
through a process of scarification to allow absorption of water. In the wild
this would occur by the gnawing actions of animals, passing through an animal's
digestive tract or abrasion by a rocky surface. In the artificial environment of
gardening this process is imitated by nicking the seed coat with a sharp knife
or rubbing with sandpaper.

If a seed has a thin coat the presence of light can either encourage or
inhibit seed growth. Smaller seeds tend to require light for germination.

Leaves A tight rosette of leaves arises from the crown after the
emergence of the characteristic cotyledonary leaves. Two kinds of leaves are
formed. The lower leaves are pinnate and linear or lanceolet, and are fine and
lacy in appearance. The upper leaves are smaller and less divided. Leaves in the
second year of growth arise from the crown and along the elongated stem.

Flower Vernalization of the plant or seed induces formation of the
inflorescence. Vernalization period is up to 6 to 8 weeks at temperatures below
50°F. Several cycles of flowering occur, producing umbel shaped inflorescence.
The first inflorescence is the largest, and is termed the king umbel, followed
by the queen and other secondary umbels. The white flowers are perfect, and
require cross-pollination for seed set. Male sterile hybrids are often used as a
seed source to decrease variability.

A little history

1599 - In his book Profitable Instructions for the Manuring,
Sowing and Planting of Kitchen Gardens, Richard Gardner
wrote: "Sow carrots in your gardens and humbly praise God for them, as for a
singular and great blessing." Seed selling was just starting to take place
at this time. Richard Gardiner who included a price list in his I599
pamphlet on vegetable and seed growing, offering vegetable seeds retail and also
wholesale - 'if any person desire to buy any store of principall carret seedes .
. . to sell for reason to others, to benefit the commonwealth, I am willing to
serve his turne better cheape then before is declared.'

This was the first printed book dedicated to growing vegetables and urged
that more carrots should be grown, because “forraine nations” like Holland were
reaping the benefit from their lucrative export trade. This was the only book
before 1773 to give detailed instructions on raising seed on a commercial scale. Mr Gardiner was a draper
from Shrewsbury and saved the lives of many poor people during a famine by
supplying them with carrots. He considered that the “large yellow Carret and the
great shorte yellow Carret were the best and fairest rootes” then grown in his
native County of Salop (Shropshire, UK).

Richard Gardiner's 'Profitable
Instructions' of 1599 gives a detailed description of vegetable seed Growing
which is particularly valuable because of its early date. The book was
written by a philanthropic market gardener and textile merchant of Shrewsbury in
an effort to encourage kitchen gardening and seed growing. In the passage quoted
below Gardiner guides the reader through carrot seed production. Having selected
the best carrots from the main crop in September and transplanted them, well
spaced, to new beds:

"Then have you nothing to doe with them untill about the last of Aprill,
at which time they will bee growne about a yard in height: then you have need to
take care of them, for the winde will easily breake them by the ground: then
must you prepare some kinde of packe-threed, or lynen threed to set about them
as a girdle, about two foote high from the earth as neede shall require by the
growing of the branches: gird some higher then other some.

Then shortly after you must have stakes in a readines, and as the
Carrets must stand one against thc other in the bed: so likewise the
stakes must stand one against the other, to everye foure Carrets two
stakes. The stakes must bee a yard and a half above thc ground, and a
sure holde within the earth for danger ofwinde: then must you prepare
packe-threed or other threed to goe from stake to stake all the length
of the bed, one course of lyrics must be about two foote high, and
another course of lynes must bee neere the top of the stakes, so that
there must be two courses of lynes on the utter side of the stakes on
both sides the bed.

Then must you have crosse lynes . . . . as the Carrets branches
doc grow they must be somewhat tended to keepe them in good order within
the lynes: this being done about the last of August, the Carret seedes
will begin to bee ripe, and as they doe change to some browne colour, so
to bee cut from time to time, untill the last bee sufficiently ripe
about the first of October: Then place the Carret seedes as you doe cut
them on a Chamber floore to drie, & when they be drie, beate the secdes
out with small staves, or best with tbe edge of a lath, and cleanse them
from the composte or refuse (as you finde best by experience) with ridle
and sive."

Further on
in this work he talks about the storage of Carrets (carrots):

"In the two
months of October and November, when you have leisure in drie weather, then
provide a vessel or wine caske, or some other: then lay on course of sand on the
bottome of the vessel two inches thicke, then a course of carret rootes, so that
the rootes do not touch one another: then another course of sand to cover those
rootes, and then another course of sand, and in this manner untill the vessell
bee full to the top, and if you have a ground seller, you may packe them in some
corner in this manner, you must cut away all the branches of the carrets close
by the roote, and somewhat of the small endes of the Carrets, and they must be
so packed in sand unwashed and about the last of December: sometime when there
is no frost, you must then unpacke them againe, and then the carret rootes will
begin to spring in the top of the roote, then if you desire to keepe them untill
a longer time, then you must pare off the upper ende of the roote, that they
cannot spring any more in the top, and then packe them again in sande as
aforesaid, so you may keepe them well till Lent or Easter.” (Source
- Garden seeds in England before the late eighteenth century: I. Seed
growing By Malcolm Thick, Agricultural History Review, 1989) -
full copy here - pdf)

Even at this early date it was recognised how valuable seed selection was,
choosing for size shape and colour - vVery much the same as today, with flavour
not high on the list!

Thompson & Morgan
is a good supplier for the
home gardener and have a tremendous variety of carrot seeds for you to try. See photos of common varieties supplied by Thompson and Morgan the leading
seed suppliers in the US and UK. Click here.

Some Sources of Carrot Seed Varieties for United States Home Gardeners - here